Water Coning Model for Horizontal Wells in High Mobility Reservoir, West Kuwait

Abstract

Water coning is a serious problem in horizontal wells in Burgan reservoir of Minagish field located in West Kuwait. The reservoir consists of massive channel sands with active bottom aquifer and having very high permeability in the order of few Darcy. The reservoir contains medium quality crude having viscosity of about 30 cp with mobility ratio of 30 to 40. The localized increase in drawdown at sand-face due to high liquid production rate results in early water breakthrough in most of the horizontal wells, even with high stand off from OWC (Oil Water Contact). After water breakthrough the water cut in the wells starts increasing strictly, resulting in by passed oil region below horizontal well. As producing water-oil ratio starts increasing, the operating cost of the well and oil production cost starts rising significantly. In one of the horizontal well of Burgan reservoir, the water cut increased to 90% over a very short period of production and the water cone could not subside even after the well was shut-in for almost three years, confirmed by running the water saturation logs in the subject well as well as in the nearby offset wells. The water saturation logs clearly indicates the oil water interface and the extent of water coning.The paper covers an analytical model developed for horizontal well to predict the critical drawdown, critical production rate, extent of water coning, time for water breakthrough and shut-in time required to subside the cone for very high mobility Burgan reservoir. The predicted results are in agreement with the actual well performance and production logging results.The detailed coning study and model presented in this paper have assisted in planning the advanced completion techniques like Inflow Control Device (ICD) and intelligent multilateral wells with ICD, ICV (Inflow Control Valve) completions to address the severe water coning problems. This allows uniform depletion of reservoir below the horizontal wells for facilitating the steady water-oil interface upward movement below the wellbore. Also the horizontal wells will be placed at optimum distance from the OWC to maximize oil recovery and minimizing the risk of by passed oil. IntroductionThe Minagish field is located in the West Kuwait (figure 1) is a north-south trending anticline with hydrocarbon contained in six major reservoirs ranging in age from early Jurassic to late Cretaceous. The Minagish field contains both sandstone and carbonate reservoirs. The Burgan sandstone reservoir consists of clastic material with minor amounts of carbonatic cements, which appear in the transition zone between continental to marine dominated environments. Generally the sand bodies, silt and shale layers are sedimented randomly within the formation. The general facies trend within the Burgan formation is from a low stand system into high stand system units. The best developed reservoir parts are having higher porosity and ultra high permeability in the order of few Darcy. The reservoir is underlain by an active aquifer causing the bottom w...

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